JP2021086370A - Inversion error measuring method of machine tool - Google Patents

Abstract

To make it possible to easily measure an inversion error of a feed shaft without using an expensive and special measuring instrument and even a machine operator who does not have a skill of operating the measuring instrument.SOLUTION: An inversion error measuring method for a machine tool executes: a first measurement step (S4) in which a touch probe is attached to a spindle (S1), a reference device is installed in a machine tool (S2) to determine the spindle (S3), and the touch probe is moved from a predetermined approach direction to the reference device to bring the touch probe into contact with the reference device, and a position of a position detector at the time of this contact is acquired; a second measurement step (S6) in which an angle of the spindle is calculated at an angle of 180 degrees with respect to an indexing angle of the spindle in the first measurement step (S5), the touch probe is moved from a direction opposite to the approach direction of the first measurement step to bring the touch probe into contact with the reference device, and a position of the position detector at the time of this contact is acquired; and an inversion error identification step (S8) in which the first measurement step and the second measurement step are performed a plurality of times to identify an inversion error of a straight axis from the acquired plurality of detection positions.SELECTED DRAWING: Figure 2

Description

The present invention relates to a method of measuring a reversal error of a feed shaft in a machine tool.

The motion error of the machine tool is transferred to the workpiece to be machined, and becomes a dimensional error or a shape error of the workpiece. One of the factors of this motion error is the inversion error (lost motion) of the feed axis. The inversion error is an error caused by a backlash element such as backlash in the feed shaft mechanism and a posture error depending on the feed direction, and the feed shaft is moved in the opposite direction with reference to the position when it is moved in one direction. This is a motion error in which the actual position is delayed with respect to the reference position for detecting the position of the feed shaft when it is moved. The reversal error may increase over time due to wear of the parts of the feed mechanism, and is often a problem because it is transferred to the workpiece as a step at the point where the feed shaft is reversed. As a countermeasure for the inversion error, there is a method of reducing it by mechanical adjustment or correction control, but in any case, it is necessary to grasp the magnitude of the inversion error.
As a conventional method for measuring the inversion error, there is a method using a ball bar measuring device as in Patent Document 1. The ball bar is a measuring instrument that can measure the distance between two balls, and each ball is attached to the machine tool via a spherical seat with a built-in magnet, and the machine tool is controlled so that the two balls move relatively in a circle. It is a measuring instrument that can diagnose the motion error of a machine tool from the measured error trajectory of the distance between two balls. In this ball bar measurement, the inversion error is observed as a step in the error locus corresponding to the inversion position of the feed shaft, and the magnitude of the inversion error can be measured from the magnitude of the step.
As another measurement method, there is also a method using a laser length measuring device as in Non-Patent Document 1. When the feed axis is operated in the plus direction and the minus direction and the positioning accuracy is measured by the laser length measuring device, the measured value in each direction is observed at an offset if there is an inversion error. The magnitude of the inversion error can be measured from this offset amount.

Japanese Unexamined Patent Publication No. 61-209857

JIS B6190-2: 2016 (ISO230-2: 2014) JIS standard "Machine tool test method general rules Part 2: Positioning accuracy test by numerical control" Standard for positioning accuracy measurement using a laser length measuring device, etc.

In the methods of Patent Document 1 and Non-Patent Document 1, it is necessary to use a special measuring instrument such as a ball bar or a laser length measuring instrument. Such measuring instruments are expensive, require certain skills to handle, and cannot be handled by anyone. Therefore, there is a problem that the inversion error of the feed shaft cannot be easily measured.

Therefore, according to the present invention, the reversal of a machine tool can easily measure the reversal error of the feed shaft without using an expensive and special measuring instrument and even a machine operator who does not have the skill of operating the measuring instrument. The purpose is to provide an error measurement method.

In order to achieve the above object, the first invention according to claim 1 is a position detection for detecting the positions of a spindle that can be rotated by mounting a tool, three or more straight shafts, and each of the straight shafts. An error measuring method for identifying a reversal error of the straight axis in a machine tool having a vessel.
The touch probe mounted on the spindle is moved from a predetermined approach direction to the reference device installed in the machine tool and brought into contact with the reference device to acquire the position of the position detector at the time of contact. The first measurement step and
The angle of the spindle is determined at an angle of 180 ° with respect to the indexing angle of the spindle in the first measurement step, and the touch probe is moved from the direction opposite to the approach direction of the first measurement step. The second measurement step of contacting the reference device and acquiring the position of the position detector at the time of contact, and
The first measurement step and the second measurement step are performed a plurality of times by changing the approach direction, and the reversal error identification step for identifying the reversal error of the straight axis is executed from the obtained plurality of detection positions. It is a feature.
According to the second aspect of the present invention, in the above configuration, in the inversion error identification step, the detection position in the first measurement step obtained for each approach direction, the detection position in the second measurement step, and the detection position in the second measurement step. It is characterized in that the width between the detection positions in each approach direction is calculated by using the vector of the approach direction, and the inversion error is obtained based on the calculated width in each approach direction.
The invention according to claim 3 relates to at least two straight axes from a plurality of detection positions obtained by performing the first measurement step and the second measurement step in at least three directions in the above configuration. It is characterized by identifying the inversion error.
The invention according to claim 4 is characterized in that, in the above configuration, the reference device has a circular or spherical shape.
In order to achieve the above object, the second invention according to claim 5 is a position detection for detecting the positions of a spindle that can be rotated by mounting a tool, three or more straight shafts, and each of the straight shafts. A reversal error measuring method for identifying the reversal error of the straight axis in a machine tool having a vessel.
A touch probe mounted on the spindle is moved from a predetermined approach direction to a reference device installed in the machine tool and brought into contact with the reference device to acquire the position of the detector at the time of contact. 1 measurement step and
The angle of the spindle is determined at an angle of 180 ° with respect to the indexing angle of the spindle in the first measurement step, and the touch probe is moved from the direction opposite to the approach direction of the first measurement step. The second measurement step of contacting the reference device and acquiring the position of the position detector at the time of contact, and
The touch probe is tilted to a posture different from the posture of the touch probe in the first measurement step so that the point of the touch probe in contact with the reference device in the first measurement step is in a predetermined approach direction. The third measurement step of determining the angle of the spindle, moving the touch probe from the approach direction to bring it into contact with the reference device, and acquiring the position of the position detector at the time of contact.
With the posture of the touch probe in the third measurement step, the angle of the spindle is calculated at an angle of 180 ° with respect to the indexing angle of the spindle in the third measurement step, and the angle of the spindle is determined in the approach direction of the third measurement step. In the fourth measurement step, the touch probe is brought into contact with the reference device from the opposite direction to acquire the position of the position detector at the time of contact.
The first measurement step and the second measurement step, and the third measurement step and the fourth measurement step are performed a plurality of times with different approach directions, and the straight axis is reversed from the obtained plurality of detection positions. It is characterized by performing an inversion error identification step to identify the error.
According to the sixth aspect of the present invention, in the above configuration, in the inversion error identification step, the detection position in the first measurement step obtained for each approach direction, the detection position in the second measurement step, and the detection position in the second measurement step. The width between the detection positions in each approach direction was calculated and calculated using the detection position in the third measurement step, the detection position in the fourth measurement step, and the vector in the approach direction. It is characterized in that the inversion error is obtained based on the width in each approach direction.
In the invention according to claim 7, in the above configuration, the first measurement step and the second measurement step are performed in at least three directions, and the third measurement step and the fourth measurement step are performed in at least two directions. It is characterized in that at least three inversion errors of the straight axis are identified from a plurality of detection positions obtained by performing the above.
The invention according to claim 8 is characterized in that, in the above configuration, the reference device has a spherical shape.

According to the present invention, a touch probe and a reference ball, which are relatively inexpensive and are equipped in many machine tools for on-machine measurement of workpieces and jigs without using expensive and special measuring instruments. The inversion error of the feed axis can be measured by using a reference device such as a ring gauge or a ring gauge. In addition, since the measurement can be performed semi-automatically only by a simple operation such as installing a reference device, even a machine operator who does not have the skill of operating the measuring device can easily measure the inversion error.

It is a schematic diagram of a 3-axis vertical machining center. It is a flowchart of the reversal error measurement method of the machine tool of 1st invention. It is a schematic diagram which shows an example of the touch probe and the reference sphere used in this invention. It is a schematic diagram of the touch probe measurement in the reversal error measurement method of this invention. It is a schematic diagram of the touch probe measurement when there is no inversion error. It is a schematic diagram of the touch probe measurement when there is an inversion error. It is a flowchart of the inversion error measurement method of the machine tool of the 2nd invention. It is a schematic diagram of the touch probe measurement in the reversal error measurement method of this invention.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
FIG. 1 is a schematic view of a 3-axis vertical machining center as an example of a machine tool.
The spindle head 2 is a straight axis and can move with two translational degrees of freedom by the X-axis and the Z-axis which are orthogonal to each other. The table 3 is a straight axis and can move with one translational degree of freedom by the Y axis orthogonal to the X and Z axes. Therefore, the spindle head 2 has three translational degrees of freedom with respect to the table 3. Each axis is provided with a position detector (not shown), and each axis is driven by a servomotor controlled by a numerical control device (not shown) based on the detection value of each position detector, and is a main axis with respect to the table 3. The relative position of the head 2 is controlled. The work piece is fixed to the table 3, a tool is attached to the main shaft 2a of the spindle head 2, and the work piece is rotated, and the work piece is made to have an arbitrary shape while interfering with the work piece. Process.

FIG. 2 shows a flowchart of the inversion error measuring method of the first invention.
In step S1, as shown in FIG. 3, a touch probe 11 having a stylus 12 having a spherical tip is attached to the spindle 2a.
The touch probe 11 is a device that outputs a signal when the stylus 12 comes into contact with an object, outputs a signal when the stylus 12 comes into contact with the object, and when the numerical control device detects the signal and receives the signal, or The position of the object can be measured by acquiring the detection position of the position detector of the straight axis at the time when the delay is taken into consideration.
In step S2, the reference sphere 13 is installed on the table 3. In the case of a machine tool in which the table 3 is fixed and the spindle head 2 operates with three translational degrees of freedom by three linear axes, unlike the machine tool of FIG. 1, the reference ball 13 is not fixed to the table 3 and is different. It may be installed in the structure.

Next, in step S3, the spindle 2a is determined so that when the tip sphere of the stylus 12 of the touch probe 11 is brought into contact with the reference sphere 13, they come into contact with each other at the same point. For example, as shown in FIG. 4, it is considered that the touch probe 11 is brought into contact with the reference sphere 13 in the XY plane formed by the X and Y axes passing through the center of the reference sphere 13. The stylus 12-1a is a case where the stylus 12-1a approaches and contacts the center of the reference sphere 13 from the plus direction of the X-axis, and the stylus 12-1a has a spindle 2a so that the reference sphere 13 contacts the white circle marker in the tip sphere of the stylus 12-1a. Determine the angle to 180 °.
Here, since the touch probe 11 has a swing with respect to the main shaft 2a and anisotropy of the sensor characteristics, when the measurement is performed with the angle of the main shaft 2a fixed, it becomes a control reference depending on the contact direction. The distance between the center of rotation of the main shaft 2a and the contact point is different. Since this variation in distance adversely affects the inversion error identification calculation described later, the spindle 2a is determined so that the tip sphere of the stylus 12 always contacts the object at the same point, so that the rotation center and the contact point of the spindle 2a are always in contact with each other. The distance between them is constant.

Next, in step S4, the touch probe 11 is brought into contact with the reference sphere 13, and the detection value of the position detector of the straight axis at the time of contact is acquired (S3, S4: first measurement step). Here, as shown in FIG. 4, the vicinity of the white circle marker on the tip sphere of the stylus 12 comes into contact with the reference sphere 13.
In step S5, the spindle 2a is determined at an angle of 180 ° with respect to the spindle angle in step S3. With respect to 12-1a in FIG. 4, the spindle angle is calculated to 0 ° as shown in 12-1b.
In step S6, the touch probe 11 is brought into contact with the reference sphere 13, and the detection value of the position detector of the straight axis at the time of contact is acquired. In the case of 12-1b of FIG. 4, the approach is made from the minus direction of the X-axis toward the center of the reference sphere 13 (S5, S6: second measurement step).
In step S7, it is determined whether all the measurements from the predetermined approach direction have been completed, and if not, the approach direction is changed and steps S3 to S6 are executed.
For example, in the case of FIG. 4, _{12-2a and 12-2b, which are 45 ° (θ 2} ) directions with respect to the X axis, and 12-, which is 90 ° direction (θ ₃ ) with respect to the X axis, that is, parallel to the Y axis. Measurements are performed on 3a and 12-3b, and 12-4a and 12-4b in the direction of 135 ° (θ _{4) with respect to the X axis.} Here, the measurement may be performed in any order, for example, measurement may be performed counterclockwise as in 12-1a, 12-2a, ... 12-4b.
In step S8, the inversion error of the straight axis is identified by using the measurement results of steps S4 and S6 (inversion error identification step). In the case of the measurement of FIG. 4, the inversion error between the X-axis and the Y-axis can be identified.

The calculation method of the inversion error between the X-axis and the Y-axis in step S8 will be described.
Consider the measurement at the contact between 12-1a and 12-1b in FIG. This measurement is called direction 1 measurement.
The X, Y, Z-axis detection values acquired by the contact of 12-1a (Xa1, Ya1, Za1), and the X, Y, Z-axis detection values acquired by the contact of 12-1b (Xb1, Yb1, Zb1). ), And the vector of the approach direction is (Vx1, Vy1, Vz1), the width W1 (FIG. 5) of the approach direction in the direction 1 measurement can be obtained from the following equation 1.
[Number 1]
W1 = (Xa1-Xb1) * Vx1 + (Ya1-Yb1) * Vy1 + (Za1-Zb1) * Vz1

Since the approach direction of the direction 1 measurement is parallel to the X axis, the approach direction vector is (1,0,0), and the width W1 is the following equation 2.
[Number 2]
W1 = Xa1-Xb1

Here, the inversion error of the X-axis included in the width W1 will be described.
FIG. 5 is a schematic view of direction 1 measurement when there is no inversion error on the X-axis. When the stylus 12-1a comes into contact with the reference sphere 13 from the X-axis plus direction, the control point 22a passing through the main axis center line, which is the control reference, coincides with the detection position 21a of the position detector. Here, let r be the distance between the contact point obtained by determining the spindle 2a at 180 ° and the center of the spindle.
Next, when the stylus 12-1b comes into contact with the reference sphere 13 from the minus direction of the X-axis, the control point 22b passing through the main axis center line, which is the control reference, coincides with the detection position 21b of the position detector. By determining the spindle at 0 °, the distance between the contact point and the center of the spindle is r, and if the diameter of the reference sphere 13 is D, W1 becomes the following number 3.
[Number 3]
W1 = D + 2r

On the other hand, FIG. 6 is a schematic view of direction 1 measurement when there is an inversion error on the X-axis. Assuming that the inversion error is an error that occurs when operating in the positive direction, the control point 22a and the detection position 21a coincide with each other in the contact in the positive direction of the X-axis as in FIG. However, in the contact in the minus direction of the X-axis, the detection position 21b'delays the control point 22b by the inversion error δx. Therefore, the width W1'when there is an inversion error is the following equation 4.
[Number 4]
W1'= D + 2r-δx

In this way, the measured value of the width in the approach direction includes the inversion error. However, since the distance r between the contact point and the center of the spindle includes the amount of swing of the spindle 2a, the anisotropy of the sensor characteristics, and the tilt of the stylus due to the delay in sensor signal output, it is necessary to grasp the accurate value of r. It is difficult. Therefore, only the inversion error is extracted by the following method.
From the results of measurement in multiple approach directions, the width of each approach direction is obtained. The X, Y, and Z axis detection values acquired by the direction i measurement (i = 1, 2, 3, 4) are (Xai, Yai, Zai), (Xbi, Ybi, Zbi), and the approach direction vector is (Vxi). , Vyi, Vzi), the width Wi in the approach direction of the direction i measurement can be obtained from the following equation 5.
[Number 5]
Wi = (Xai-Xbi) * Vxi + (Yai-Ybi) * Vyi + (Zai-Zbi) * Vzi
When the approach direction of each measurement in FIG. 4 is represented by the angle θi from the X axis in the XY plane, each component of the approach direction vector of the direction i measurement is the following equation 6.
[Number 6]
Vxi = cosθi
Vyi ＝ sinθi
Vzi = 0

Substituting the number 6 into the number 5, the width Wi in the approach direction of the direction i measurement becomes the next number 7.
[Number 7]
Wi = (Xai-Xbi) * cosθi + (Yai-Ybi) * sinθi
Using the obtained n Wis (n = 4 in this example), the inversion error δx on the X-axis and the inversion error δy on the Y-axis are obtained from the following equation 8.

The above measurement is performed in the same manner for the YZ plane formed by the Y and Z axes and the ZX plane formed by the Z and X axes, and the same calculation method is performed using the measurement results to perform the same calculation method for the Y and Z axes, respectively. The inversion error of, and the inversion error of the Z and X axes can be obtained.
In this example, a spherical reference sphere is used as the reference device, but a circular reference device such as a cylindrical block may be used. Further, a reference device such as a ring gauge whose inner diameter is a measurement target may be used. In the case of inner diameter measurement, there is no essential difference except that the approach direction is reversed, and the inversion error can be obtained by the same calculation method.

As described above, according to the reversal error measurement method of the above embodiment, the touch probe 11 mounted on the spindle 2a is moved from a predetermined approach direction with respect to the reference ball 13 (reference device) installed in the machine tool. The angle of the spindle 2a is set to an angle of 180 ° with respect to the indexing angle of the spindle 2a in the first measurement step of contacting the reference sphere 13 to acquire the position of the position detector at the time of contact and the first measurement step. The second measurement step and the first measurement step of indexing and moving the touch probe 11 from the direction opposite to the approach direction of the first measurement step to bring the touch probe 11 into contact with the reference ball 13 and acquiring the position of the position detector at the time of contact. The second measurement step is performed a plurality of times, and the reversal error identification step for identifying the reversal error of the straight axis is executed from the obtained plurality of detection positions.
With this configuration, the touch probe 11 and the reference ball 13 are relatively inexpensive and are equipped in many machine tools for on-machine measurement of workpieces and jigs without using expensive and special measuring instruments. And can be used to measure the inversion error of the feed axis. Further, since the measurement can be performed semi-automatically only by a simple operation such as installing the reference ball 13, even a machine operator who does not have the skill of operating the measuring instrument can easily measure the inversion error.

Next, a method of simultaneously identifying the inversion errors of the X, Y, and Z axes will be described with reference to the flowchart of FIG. 7.
Since steps S1 and S2 are the same as those in FIG. 2, description thereof will be omitted.
Here, in S10 after step S2, the posture of the touch probe 11 is changed to a predetermined angle. To change the posture of the touch probe 11, a machine tool capable of changing the posture of the spindle 2a is used, or the touch probe 11 itself is provided with a mechanism capable of changing the posture, or a plurality of touch probes having different postures are used. There is a method, and any of them may be used.
The posture of the j-th touch probe is determined by rotating βj and γj in this order when viewed from the touch probe, with the angle βj around the Y-axis and the angle γj around the Z-axis.
As the first posture, β1 = 0 ° and γ1 = 0 °, that is, the posture in which the touch probe 11 is perpendicular to the XY plane is measured. The posture of this touch probe is called posture 1. Since the measurement of the posture 1 is the same as the measurement on the XY plane described above and the steps S3 to S7 are the same, the description thereof will be omitted.

After the measurement in all directions is completed in S7, in step S11, it is determined whether all the measurements in the predetermined postures are completed. If not, the process returns to S10, the posture of the touch probe is changed, and the steps S3 are started. Execute S7 (third and fourth measurement steps).
For example, β2 = 90 ° and γ2 = 0 ° are set as the second posture, and measurement is performed in four directions on the ZX plane as shown in FIG.
In step S12, the inversion errors of the X-axis, Y-axis, and Z-axis are identified by using the measurement results of the plurality of postures and directions.

A method of simultaneously calculating the inversion error of the X, Y, and Z axes in step S12 will be described.
When measurement is performed in n directions in each of m postures, the detected values acquired in the direction i measurement (i = 1, 2, ... n) in the posture j (j = 1, 2, ... m). Is (Xaji, Yaji, Zaji), (Xbji, Ybji, Zbji), and the approach direction vector of each measurement is (Vxji, Vyji, Vzji), the width Wji of each approach direction is obtained by the following equation 9.
[Number 9]
Wji = (Xaji-Xbji) * Vxji + (Yaji-Ybji) * Vyji + (Zaji-Zbji) * Vzji
Assuming that the angle of the direction i measurement of the posture j is θji, each component of the approach direction vector has the following number tens.
[Number 10]
Vxji ＝ cosθji ＊ cosβj ＊ cosγj−sinθi ＊ sinγj
Vyji ＝ cosθji ＊ cosβj ＊ sinγj ＋ sinθi ＊ cosγj
Vzji ＝ −cosθi ＊ sinβj

Using the obtained m × n Wjis, the inversion error δx on the X-axis, the inversion error δy on the Y-axis, and the inversion error δz on the Z-axis are obtained from the following equation 11.

Assuming that the distance between the contact point in the posture j and the center of the spindle is rj, the inversion error is obtained by the following equation 12.

As described above, according to the reversal error measurement method of the above embodiment, in addition to the first and second measurement steps, the touch probe 11 is tilted to a posture different from the posture of the touch probe 11 in the first measurement step, and the first step is performed. In the measurement step, the angle of the spindle 2a is determined so that the point of the touch probe 11 in contact with the reference sphere 13 is in the predetermined approach direction, and the touch probe 11 is moved from the approach direction to come into contact with the reference sphere 13. The spindle at an angle of 180 ° with respect to the indexing angle of the spindle 2a in the third measurement step while maintaining the postures of the touch probe 11 in the third measurement step for acquiring the position of the position detector at the time of contact and the third measurement step. The fourth measurement step of determining the angle of 2a, bringing the touch probe 11 into contact with the reference sphere 13 from the direction opposite to the approach direction of the third measurement step, and acquiring the position of the position detector at the time of contact is executed. It is designed to do.
With this configuration, inversion errors on the three straight axes X, Y, and Z axes can be identified at the same time.

The present invention is applicable not only to the above-described vertical machining center but also to other machine tools such as a horizontal machining center.

1 ... bed, 2 ... spindle head, 2a ... spindle, 3 ... table, 11 ... touch probe, 12 ... stylus, 13 ... reference sphere.

Claims (8)

Error measurement for identifying the reversal error of the straight shaft in a machine tool having a spindle that can be rotated by mounting a tool, three or more straight shafts, and a position detector that detects the position of each of the straight shafts. It ’s a method,
The touch probe mounted on the spindle is moved from a predetermined approach direction to the reference device installed in the machine tool and brought into contact with the reference device to acquire the position of the position detector at the time of contact. The first measurement step and
The angle of the spindle is determined at an angle of 180 ° with respect to the indexing angle of the spindle in the first measurement step, and the touch probe is moved from the direction opposite to the approach direction of the first measurement step. The second measurement step of contacting the reference device and acquiring the position of the position detector at the time of contact, and
A reversal error identification step for identifying the reversal error of the straight axis from the obtained plurality of detection positions by performing the first measurement step and the second measurement step a plurality of times with different approach directions.
A method for measuring the inversion error of a machine tool, which is characterized by executing. In the inversion error identification step, each of the approaches is used by using the detection position in the first measurement step obtained for each approach direction, the detection position in the second measurement step, and the vector of the approach direction. The method for measuring a reversal error of a machine tool according to claim 1, wherein the width between the detection positions in each direction is calculated, and the reversal error is obtained based on the calculated width in each approach direction. Claim 1 is characterized in that at least two inversion errors of the straight axis are identified from a plurality of detection positions obtained by performing the first measurement step and the second measurement step in at least three directions. Or the method for measuring the reversal error of a machine tool according to 2. The method for measuring a reversal error of a machine tool according to any one of claims 1 to 3, wherein the reference device has a circular or spherical shape. In a machine tool having a spindle that can be rotated by mounting a tool, three or more straight shafts, and a position detector that detects the position of each of the straight shafts, a reversal error that identifies the reversal error of the straight shaft. It ’s a measurement method,
A touch probe mounted on the spindle is moved from a predetermined approach direction to a reference device installed in the machine tool and brought into contact with the reference device to acquire the position of the detector at the time of contact. 1 measurement step and
The angle of the spindle is determined at an angle of 180 ° with respect to the indexing angle of the spindle in the first measurement step, and the touch probe is moved from the direction opposite to the approach direction of the first measurement step. The second measurement step of contacting the reference device and acquiring the position of the position detector at the time of contact, and
The touch probe is tilted to a posture different from the posture of the touch probe in the first measurement step so that the point of the touch probe in contact with the reference device in the first measurement step is in a predetermined approach direction. The third measurement step of determining the angle of the spindle, moving the touch probe from the approach direction to bring it into contact with the reference device, and acquiring the position of the position detector at the time of contact.
With the posture of the touch probe in the third measurement step, the angle of the spindle is calculated at an angle of 180 ° with respect to the indexing angle of the spindle in the third measurement step, and the angle of the spindle is determined in the approach direction of the third measurement step. In the fourth measurement step, the touch probe is brought into contact with the reference device from the opposite direction to acquire the position of the position detector at the time of contact.
The first measurement step and the second measurement step, and the third measurement step and the fourth measurement step are performed a plurality of times with different approach directions, and the straight axis is reversed from the obtained plurality of detection positions. Inversion error identification step to identify the error and
A method for measuring the inversion error of a machine tool, which is characterized by executing. In the inversion error identification step, the detection position in the first measurement step obtained for each approach direction, the detection position in the second measurement step, the detection position in the third measurement step, and the first. Using the detection position in the four measurement steps and the vector in the approach direction, the width between the detection positions in each approach direction is calculated, and the inversion error is calculated based on the calculated width in each approach direction. The reversal error measuring method for a machine tool according to claim 5, wherein the method is obtained. From a plurality of detection positions obtained by performing the first measurement step and the second measurement step in at least three directions and performing the third measurement step and the fourth measurement step in at least two directions. The method for measuring a reversal error of a machine tool according to claim 5 or 6, wherein at least three reversal errors of the straight axis are identified. The method for measuring a reversal error of a machine tool according to any one of claims 5 to 7, wherein the reference device has a spherical shape.

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